Memcached vs Redis: A detailed comparison

Table of Contents

Introduction

In-memory data stores are fundamental components of modern, data-intensive architectures, especially those that require minimal latency. They store data directly in the system’s memory (RAM) instead of on disk, which results in significantly faster read and write operations.

Redis and Memcached are two prominent in-memory stores, renowned for their speed, efficiency, and flexibility. However, they possess distinct features and cater to different use cases. If you're undecided between the two, don’t worry — in this article, we will present a detailed comparative analysis to help you select the ideal solution for your specific needs.

Background information

Let’s start with brief overviews of both data platforms.

Memcached

Memcached is a popular open-source, in-memory key-value store. It is primarily used for caching purposes to speed up dynamic web applications by reducing the need to query databases for every request. Although not as feature-rich as Redis, Memcached is known for its simplicity and high performance in handling large volumes of data.

Memcached was developed by Brad Fitzpatrick in 2003 to improve the performance of LiveJournal, a social networking service. Owing to its ease of use and effectiveness, it quickly became a standard caching solution for many high-traffic websites and applications.

Memcached is licensed under the BSD 3 Revised License, which allows developers to use, modify, and distribute Memcached freely. However, the license disclaims any warranty, express or implied, and limits liability for any damages arising from the use of Memcached.

Redis

Redis is an in-memory data structure store used as a cache, message broker, and database. Redis supports several data structures, such as strings, hashes, lists, sets, and sorted sets, which makes it versatile for different use cases.

Redis was created by Salvatore Sanfilippo in 2009 to improve the performance of his startup’s web application. Over the years, it gained popularity for its speed and extensibility, and has since evolved with contributions from a large community of developers to become one of the most widely used in-memory stores.

For many years, Redis was an open-source software with a permissive BSD-3 license. However, in March 2024, Redis underwent a significant licensing change. It’s now available under either the Server-Side Public License or the Redis Source Available License. This essentially means that it’s no longer open-source. Under the new license, cloud platforms that host Redis offerings will not be allowed to use the Redis code without first entering into licensing terms with Redis Ltd, the company that manages the software.

Differences in key features

In the following sections, we will compare the features of Redis vs Memcached across various categories.

Data structures

Memcached

Memcached is a relatively simple key-value store. It primarily supports strings and integers as data types. This simple design contributes to its high performance, but also limits its applicability to certain use cases.

Redis

Redis, on the other hand, offers a much richer set of data structures, including:

  • Strings: Simple key-value pairs.
  • Hashes: Ideal for storing objects.
  • Lists: Linked lists for queue and stack implementations.
  • Sets: Unordered collections of unique elements.
  • Sorted sets: Sets ordered by a score, useful for ranking.
  • Bitmaps: Efficient storage and manipulation of bits.
  • HyperLogLogs: Probabilistic data structures for estimating cardinality.
  • Streams: Log-based data structure for storing and processing streams of data.
  • Geospatial indexes: Handling location-based data.

Security

Memcached

Memcached doesn’t have many built-in security mechanisms.

  • Memcached supports SASL (Simple Authentication and Security Layer) for authentication, but does not provide end-to-end encryption. Additionally, using SASL requires that the clients also support SASL, which can complicate integration, especially with modern apps.
  • Memcached does not natively support encryption. To encrypt data in transit, you would need to use additional tools or establish encrypted tunnels (such as VPNs or SSL/TLS proxies).
  • It lacks built-in access control mechanisms. For the most part, security relies on network-level restrictions to control which clients can access the server.

Redis

On the other hand, Redis offers several security controls that make it an enterprise-grade solution:

  • Redis supports password-based authentication. By setting a password in the configuration file, you can require clients to authenticate before performing any operations.
  • Another way to implement access control in Redis is via ACLs (access control lists). With ACLs, you can specify which commands users can execute, and which keys they can access.
  • It also offers TLS (Transport Layer Security) to encrypt data in transit. This ensures that data is not exposed to eavesdropping as it’s transmitted between clients and servers.

Persistence

Memcached

Memcached is designed as a volatile cache with no built-in persistence mechanisms. It stores data in memory only, meaning that all data is lost if the server is restarted or crashes. This makes Memcached more suited for scenarios where data durability isn’t necessary, such as temporary caching where data can be regenerated if lost.

Redis

Redis, in contrast, has evolved over time to offer multiple options for persistence.

  • Snapshotting (RDB): Redis can create point-in-time snapshots of your data set at specified intervals. These snapshots are stored in an RDB (Redis Database) file. This file can be used to restore the database in case of a restart or failure.
  • Append-Only File (AOF): Redis can also use an append-only file, where every write operation is logged. The AOF file can be replayed to rebuild the data set after a crash or restart.
  • Hybrid persistence: This methodology combines RDB snapshots with AOF logs to speed up restart times. The RDB snapshot is used to restore most of the data quickly, and then the AOF log is applied for recent changes.
  • No persistence: You can also run Redis in a mode where no data is persisted to disk.

Scalability

Memcached

Memcached uses a technique called consistent hashing, where the client determines which Memcached server to use based on the key. This allows Memcached to scale horizontally by introducing more nodes to the setup. However, Memcached does not natively support replication. High availability and redundancy must be managed at the application level or through additional tools.

Redis

Redis is packed with several features for high scalability and availability:

  • Sharding: Redis supports automatic sharding through Redis Cluster, which distributes data across multiple Redis nodes. This simplifies horizontal scaling.
  • Replication: Redis supports master-slave replication, where data is copied from a master node to one or more replica nodes. This improves read scalability by allowing read operations to be offloaded to replicas, while the writes are handled by the master.
  • Partitioning: Redis also supports manual partitioning, which allows developers to divide data across multiple Redis instances.
  • Sentinel: Redis Sentinel provides high availability by monitoring Redis instances, detecting failures, and automatically promoting a replica to master if the current master fails.

Performance

Memcached

Memcached is known for extremely fast data retrieval of data stored in memory. Owing to its multi-threaded architecture, Memcached can handle multiple operations simultaneously across several threads. This allows it to take advantage of multi-core processors and serve a high number of concurrent requests.

Moreover, Memcached is a lightweight application, with minimal processing overhead, which enables it to serve requests quickly and efficiently.

Redis

Redis is also designed for high performance. It uses a single-threaded event loop, which simplifies concurrency management and reduces context switching overhead to deliver predictable and consistent performance.

It supports pipelining, where multiple commands can be sent to the server at once, without having to wait for individual responses. This reduces the latency of network round trips.

Memory management

Memcached

Here’s a look at how Memcached manages memory:

  • Memory allocation: Memcached uses slab allocation; i.e. it divides memory into fixed-size chunks (slabs) to reduce fragmentation and efficiently manage memory for different object sizes.
  • Eviction policies: Memcached supports basic eviction policies, like LRU (least recently used). With an LRU policy, when memory is full, Memcached evicts the least recently used items to free up space for new data.
  • Memory limit: The memory allocated to Memcached is defined at startup, and it cannot dynamically resize without restarting the server.

Redis

Redis includes different advanced memory management features to optimize memory usage:

  • Memory efficiency: Redis uses various data encoding techniques to reduce memory footprint, such as compact encoding for small keys and values.
  • Eviction policies: Redis provides configurable eviction policies for managing memory when it reaches its limit, including:
    • noeviction: Does not evict when the memory limit is reached, but rather returns an error.
    • allkeys-lru: Evicts the least recently used (LRU) keys from the entire data set.
    • volatile-lru: Evicts the least recently used (LRU) keys from those with an expiration set.
    • allkeys-random: Evicts random keys from the entire data set.
  • Memory fragmentation: Redis uses memory allocation strategies to minimize fragmentation. For example, it leverages jemalloc (a memory allocator) that manages fragmentation better than the default allocator.

Differences in use cases

Next, let’s explore the different use cases in which each platform excels.

Memcached

Memcached is primarily used for:

  • Caching: It can cache database query results, API responses, and other frequently accessed data to improve application performance.
  • Session management: It can store user sessions, though it lacks some of the advanced features of Redis.
  • Simple key-value storage: It’s also useful for scenarios where a basic key-value store is needed without complex data structures.

Redis

Redis’s support for a variety of data structures and features makes it suitable for a wide range of use cases:

  • Caching: Used to cache frequently accessed data to reduce database load and improve response times.
  • Session management: Ideal for storing user sessions due to its fast read and write operations, and support for even complex data structures.
  • Real-time analytics: Suitable for real-time data processing and analytics using data structures like streams and sorted sets.
  • Pub/sub messaging: Provides a publish/subscribe messaging system for real-time communication between applications.
  • Leaderboard and ranking: Uses sorted sets to manage and retrieve ranking information quickly.
  • Geospatial applications: Manages location-based data and performs geospatial queries with its geospatial indexing features.

Differences in community, support, and documentation

Memcached

Memcached has a strong and active community, though it is somewhat smaller compared to that of Redis. The community provides support through forums, mailing lists, and GitHub. There is no official commercial support directly from the Memcached project, but certain companies and cloud providers offer managed Memcached services with support.

Memcached has good documentation, including installation guides, basic usage instructions, and API references. That said, its documentation is less extensive compared to Redis.

Redis

Redis has a large and active community with a wide range of contributors, users, and third-party tools. The community frequently contributes to improvements, bug fixes, and new features. There are numerous forums, mailing lists, and online communities where users can seek support and share knowledge. For enterprise-level assistance, Redis Ltd offers commercial support, including consulting, training, and dedicated technical assistance.

Additionally, Redis has comprehensive and well-organized documentation available on its official website. It includes detailed guides, tutorials, and API references for all features, data structures, and deployment strategies.

Pros and cons of Redis and Memcached

Finally, here’s a summarization of the pros and cons of Redis and Memcached to help you determine the tool that might be better suited for your use case.

Memcached

Pros
  • Easy to set up and use with a straightforward key-value storage model.
  • Optimized for speed with low latency and efficient memory management, but mainly for simple caching.
  • Can handle multiple operations concurrently across several threads by leveraging multi-core processors.
  • Minimal processing overhead, as it focuses solely on caching with a simple API.
Cons
  • Only supports basic key-value pairs, and lacks the rich data structures available in Redis.
  • Does not offer data persistence; all data is lost if the server restarts or crashes.
  • Lacks built-in replication and high availability features; these must be managed externally.
  • Does not contain essential security measures like end-to-end encryption and fine-grained access control.

Redis

Pros
  • Supports various data structures (strings, lists, sets, sorted sets, hashes, etc.), which makes it versatile for different use cases.
  • Offers multiple persistence methods (RDB, AOF, hybrid) to ensure data durability and recovery.
  • Includes features like Redis Sentinel and Redis Cluster for high availability, failover, and horizontal scaling.
  • Caters to wide-ranging functionalities such as pub/sub messaging, geospatial indexing, and Lua scripting.
  • Delivers high performance with sub-millisecond latency and efficient memory management.
  • Packed with an extensive list of security features, including authentication, ACLs, TLS support, and protected mode.
Cons
  • Generally requires more memory and CPU compared to Memcached.
  • More complex to configure and manage due to the variety of features.
  • Even though the single-threaded model simplifies concurrency, it can be a limitation for very high throughput scenarios without appropriate sharding.
  • No longer open-source, which makes it more expensive to obtain, deploy, and manage.

Migrating from Memcached to Redis

If you are looking to migrate from Memcached to Redis, here’s a general overview of how to go about it:

  • Analyze the data stored in Memcached, including data types, sizes, and access patterns. This will help you determine the appropriate Redis data structures.
  • Deploy Redis on your infrastructure. Follow installation guides and configure it according to your needs. For example, you may set up persistence, replication, and ACLs.
  • Develop a script or tool to transfer data from Memcached to Redis. You can use Redis's pipeline feature for efficient data loading. Here, you may also need to transform the data to match Redis's data structures. For example, you may convert simple key-value pairs into Redis hashes or lists if required by your application.
  • Post-transfer, verify the integrity of the loaded data.
  • Update your application’s data access code to use Redis instead of Memcached. Replace Memcached client libraries with Redis client libraries and adapt the code to handle Redis commands and data structures.
  • Run comprehensive tests to ensure that your application functions correctly with Redis. Check for performance, correctness, and compatibility.
  • Adjust your caching strategies to leverage Redis features, such as advanced eviction policies or pub/sub models.
  • Keep an eye on Redis performance and adjust configurations if needed. Monitor for any issues that may arise during and after migration. Dedicated tools, such as the Redis Monitoring Solution by Site24x7, can be used for this purpose.
  • Fine-tune Redis configuration and application code based on performance and usage patterns. For example, if you notice high memory usage or latency issues, adjust Redis configurations such as max memory policies, eviction strategies, or persistence settings to boost performance.

Conclusion

Redis and Memcached are both reliable in-memory data stores that have stood the test of time. Redis is undeniably more feature-rich than Memcached, but recent licensing changes may affect its commercial viability compared to Memcached. On the other hand, even though Memcached is more lightweight and easier to configure than Redis, its data structure support pales in comparison to that of Redis.

Ultimately, choosing between Redis and Memcached depends on your application requirements. If your workloads require raw speed and simplicity, Memcached can be a better choice. However, if your application relies on complex data structures, persistence, and a wider range of operations, Redis would be the more versatile option.

Carefully evaluate the trade-offs between performance, feature set, and operational complexity to make the right call. Whichever platform you choose, remember to monitor its health and performance to ensure business continuity. Site24x7 offers dedicated monitoring tools for both Memcached and Redis.

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